Mobile terminal with down-link synchronisation via an iterative correlation system

ABSTRACT

Mobile terminals ( 10 ) with down-link synchronization through detection of code signals used in Time Division—Synchronous Code Division Multiple Access (TD-SCDMA) telecommunication systems and/or in Universal Mobile Terrestrial System—Frequency Division Duplexing (UMTS-FDD) telecommunication systems detect these code signals by using a correlator system ( 1 ) for making sliding correlations, which require much processing capacity. By introducing a controller ( 3 ) for making iterative correlations in combination with an adaptable information compactness, the processing capacity can be reduced a lot. Preferably, comparator ( 4 ) compares correlation results with thresholds, with said controller ( 3 ) selecting smaller parts within said part of said input signal for a next correlation. By increasing the information compactness of said smaller parts, the accuracy of a next correlation is improved. A down-sampler ( 5 ) is used for controlling said information compactness, with a down-sampling factor being decreased for a next correlation to increase said information compactness for said next correlation.

The invention relates to a correlation system for correlating at least apart of an input signal with at least a part of at least one codesignal.

The invention also relates to a mobile terminal with down-linksynchronisation through detection of at least one code signal, whichmobile terminal comprises a receiver for receiving a radio signal andfor converting said radio signal into an input signal and comprises acorrelation system coupled to said receiver for correlating at least apart of said input signal with at least a part of at least one codesignal, and to a method for correlating at least a part of an inputsignal with at least a part of at least one code signal, and to aprocessor program product for correlating at least a part of an inputsignal with at least a part of at least one code signal, and to a methodfor down-link synchronisation through detection of at least one codesignal, which method comprises the steps of receiving a radio signal andof converting said radio signal into an input signal and of correlatingat least a part of said input signal with at least a part of at leastone code signal.

Such a correlation system and such a mobile terminal are for exampleused in Time Division—Synchronous Code Division Multiple Access(TD-SCDMA) telecommunication systems and/or in Universal MobileTerrestrial System—Frequency Division Duplexing (UMTS-FDD)telecommunication systems, in which a synchronisation code (code signal)is repeatedly sent in a down-link synchronisation channel to a mobileterminal. The mobile terminal must detect this synchronisation coderapidly and accurately without any prior knowledge, apart from thesynchronisation code itself. Thereto, the mobile terminal comprises acorrelation system having for example a matched filter for makingsliding correlations. After several sliding correlations, the bestcorrelation result (like for example the highest correlation peak)indicates the final result.

A prior art correlation system is known from U.S. Pat. No. 5,982,763.The receiver (unit 602 in FIG. 10 of U.S. Pat. No. 5,982,763) in themobile terminal receives a radio signal originating from a base stationand comprising the code signal, and converts said radio signal into theinput signal. Then the correlation system (unit 102 in FIG. 1 of U.S.Pat. No. 5,982,763) coupled to said receiver correlates said inputsignal with one or more code signals which each have been previouslystored in a terminal's memory. Thereto said correlation system comprisesone or more correlators for making said sliding correlations.

The known correlation system is disadvantageous, inter alia, due torequiring too much processing capacity. Said code signal is repeatedlysent in the down-link channel, thereby using either each entiretime-slot or just a part of each time-slot of this down-link channel,with the other part of each time-slot then for example being used fordata Then per time-slot said sliding correlations must be performed,with each sliding correlation comprising the sliding (chip for chip) ofthe length of a code signal through a predefined part of said inputsignal. Such a computational complexity is extremely high, due to eachsliding correlation per chip-sliding comprising one or morecalculations.

It is an object of the invention, inter alia, of providing a correlationsystem as

efined in the preamble which requires less processing capacity.

The correlation system according to the invention is characterised inthat said

rrelation system comprises a controller for controlling said correlationsystem for

erforming iterative correlations and for adapting at least aninformation compactness of at

ast a part of at least one of said signals for a next correlation.

By introducing iterative correlations, the results of previouscorrelations can

used for (improving) next correlations. And by introducing an adaptableinformation

mpactness (information density) of at least one of said signals, theprocessing capacity can

reduced a lot, under the condition that a result of a previouscorrelation can still be used

r (improving) a next correlation. This allows iterative correlations tobe performed in an

timal way.

Said next correlation will generally but not exclusively be a subsequent

rrelation. So, it is not to be excluded that one or more furthercorrelations are situated

etween a previous correlation and a next correlation.

The invention is based upon an insight, inter alia, that complicatedcorrelations

n be replaced by less complicated iterative correlations, and is basedupon a basic idea,

ter alia, that the complexity of a correlation can be amended byadapting the information

mpactness (information density).

The invention solves the problem, inter alia, of providing a correlationsystem

defined in the preamble which requires less processing capacity.

A first embodiment of the correlation system according to the inventionas defined in claim 2 is advantageous in that said correlation systemcomprises a comparator for comparing a correlation result with at leastone threshold and in response generating a comparison result, with saidcontroller, in dependence of said comparison result, selecting smallerparts within said part of said input signal for a next correlation.

By, in dependence of said comparison result, selecting smaller parts,like for example four smaller parts each being about 10% of said part ofsaid input signal and each comprising a correlation result (like forexample a correlation peak) exceeding said threshold, a next correlationjust uses 4×10%=40% of the original part for finding the bestcorrelation result (like for example the highest correlation peak) withreduced processing capacity (being 40% of the original processingcapacity).

A second embodiment of the correlation system according to the inventionas defined in claim 3 is advantageous in that the informationcompactness of at least said smaller parts is increased for a nextcorrelation.

By increasing the information compactness (information density) of saidsmaller parts, the accuracy of this next correlation is improved. Incase of said information compactness (information density) of said foursmaller parts being doubled, said next correlation still uses just 40%of the original part, with the reduced processing capacity still beinglower than the original processing capacity (but now being 80% of theoriginal processing capacity).

A third embodiment of the correlation system according to the inventionas defined in claim 4 is advantageous in that said correlation systemcomprises a down-sampler for generating said input signal and coupled toan output of an analog-to-digital converter for, in dependence of saidcomparison result, down-sampling an output signal of saidanalog-to-digital converter with a down-sampling factor.

By introducing said down-sampler, like for example a memory for storingy samples and for reading out y/2 or y/4 etc. samples, or like forexample a switch for letting pass every second or fourth etc. sample andfor blocking all other samples, the information compactness (informationdensity) can be controlled easily.

A fourth embodiment of the correlation system according to the inventionas defined in claim 5 is advantageous in that said down-sampling factoris decreased for a next correlation to increase said informationcompactness for said next correlation.

By decreasing said down-sampling factor for next correlations, like forexample from a factor eight via a factor four and a factor two to afactor one, said information compactness (information density) for thesenext correlations is increased. Said decreasing of said down-samplingfactor corresponds with increasing a down-sampling rate/frequency, dueto said down-sampling factor and said down-sampling rate/frequency beingreciprocal. The minimum value of the down-sampling factor is one, whichmeans that the maximum value of the down-sampling rate/frequency isequal to the full over-sampling rate/frequency. Together with saidselection of said smaller parts, the iterative correlations are nowperformed in the most optimal way. Of course, after the down-samplingfactor has reached its minimum value one, the down-samplingrate/frequency will be kept equal to this full over-samplingrate/frequency, with further selections of smaller parts still belongingto the possibilities and therefore not to be excluded.

For each one of said embodiments, said next correlation will generallybut not exclusively be a subsequent correlation. So, it is not to beexcluded that one or more further correlations are situated between aprevious correlation and a next correlation.

Embodiments of the mobile terminal according to the invention, of themethod for correlating according to the invention, of the processorprogram product according to the invention and of the method fordown-link synchronisation according to the invention correspond with theembodiments of the correlation system according to the invention.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments(s) described hereinafter.

FIG. 1 illustrates in block diagram form a mobile terminal according tothe invention comprising a correlator system according to the invention,and

FIG. 2 illustrates a flow chart for elucidating a method according tothe invention and a processor program product according to theinvention.

FIG. 1 illustrates in block diagram form a mobile terminal 10 comprisinga correlator system 1 according to the invention. Correlator system 1comprises a controller 3 for controlling a down-sampler 5, a correlator2 and a comparator 4. An input of down-sampler 5 forms an input ofcorrelator system 1, and an output of down-sampler 5 is coupled to aninput of correlator 2, of which an output is coupled to an input ofcomparator 4. Control in/outputs of controller 3 are coupled to controlin/outputs of down-sampler 5, correlator 2 and comparator 4. A controlinput of controller 3 is coupled to the input of correlator system 1. Afurther control in/output of controller 3 is coupled to a controlin/output of a decoder 13, of which an input is coupled to said input ofcorrelator system 1 and of which an output is coupled to an input of adetector 14, of which an output for generating decoded/detected data iscoupled to a further control input of controller 3. Correlator 2 forexample comprises one or more matched filters.

Mobile terminal 10 further comprises, in addition to said correlatorsystem 1, decoder 13 and detector 14, a receiver 11 of which an input iscoupled to coupled to an antenna and of which an output is coupled to aninput of an analog-to-digital converter 12, of which an output iscoupled to said input of correlator system 1 and to the input of decoder13.

According to prior art, the mobile terminal 10 with down-linksynchronisation through detection of at least one code signal comprisesa receiver 11 for receiving a radio signal and for converting said radiosignal into an input signal and comprises a correlation system 1 coupledto said receiver 11 for correlating at least a part of said input signalwith at least a part of at least one code signal.

Such a correlation system 1 and such a mobile terminal 10 are forexample used in Time Division—Synchronous Code Division Multiple Access(TD-SCDMA) telecommunication systems and/or in Universal MobileTerrestrial System—Frequency Division Duplexing (UMTS-FDD)telecommunication systems, in which a synchronisation code (code signal)is repeatedly sent in a down-link synchronisation channel to a mobileterminal 10. The mobile terminal 10 must detect this synchronisationcode rapidly and accurately without any prior knowledge, apart from thesynchronisation code itself. Thereto, the mobile terminal 10 comprises acorrelation system 1 having for example a matched filter for makingsliding correlations. After several sliding correlations, the bestcorrelation result (like for example the highest correlation peak)indicates the final result.

A prior art correlation system 1 is known from U.S. Pat. No. 5,982,763.The receiver 11 (unit 602 in FIG. 10 of U.S. Pat. No. 5,982,763) in themobile terminal 10 receives a radio signal originating from a basestation and comprising the code signal, and converts said radio signalinto the input signal. Then the correlation system 1 (unit 102 in FIG. 1of U.S. Pat. No. 5,982,763) coupled to said receiver 11 correlates saidinput signal with one or more code signals which each have beenpreviously stored in a terminal's memory for example forming part ofcontroller 3. Thereto said correlation system 1 comprises one or morecorrelators 2 for making said sliding correlations.

The known correlation system 1 is disadvantageous, inter alia, due torequiring too much processing capacity. Said code signal is repeatedlysent in the down-link channel, thereby using either each entiretime-slot or just a part of each time-slot of this down-link channel,with the other part of each time-slot then for example being used fordata. Then per time-slot said sliding correlations must be performed,with each sliding correlation comprising the sliding (chip for chip) ofthe length of a code signal through a predefined part of said inputsignal. Such a computational complexity is extremely high, due to eachsliding correlation per chip-sliding comprising one or morecalculations.

It is an object of the invention, inter alia, of providing a correlationsystem 1 as defined before which requires less processing capacity.

The correlation system 1 according to the invention is characterised inthat said correlation system 1 comprises a controller 3 for controllingsaid correlation system for performing iterative correlations and foradapting at least an information compactness of at least a part of atleast one of said signals for a next correlation.

By introducing iterative correlations, the results of previouscorrelations can be used for (improving) next correlations. And byintroducing an adaptable information compactness (information density)of at least one of said signals, the processing capacity can be reduceda lot, under the condition that a result of a previous correlation canstill be used for (improving) a next correlation. This allows iterativecorrelations to be performed in an optimal way.

Said next correlation will generally but not exclusively be a subsequentcorrelation. So, it is not to be excluded that one or more furthercorrelations are situated between a previous correlation and a nextcorrelation.

A first embodiment of the correlation system 1 according to theinvention is advantageous in that said correlation system 1 comprises acomparator 4 for comparing a correlation result with at least onethreshold and in response generating a comparison result, with saidcontroller 3, in dependence of said comparison result, selecting smallerparts within said part of said input signal for a next correlation.

By, in dependence of said comparison result, selecting smaller parts,like for example four smaller parts each being about 10% (or 1%) of saidpart of said input signal and each comprising a correlation result (likefor example a correlation peak) exceeding said threshold, a nextcorrelation just uses 4×10% (or 1%)=40% (or 4%) of the original part forfinding the best correlation result (like for example the highestcorrelation peak) with reduced processing capacity (being 40% (or 4%) ofthe original processing capacity).

A second embodiment of the correlation system 1 according to theinvention is advantageous in that the information compactness of atleast said smaller parts is increased for a next correlation.

By increasing the information compactness (information density) of saidsmaller parts, the accuracy of this next correlation is improved. Incase of said information compactness (information density) of said foursmaller parts being doubled, said next correlation still uses just 40%(or 4%) of the original part, with the reduced processing capacity stillbeing lower than the original processing capacity (but now being 80% (or8%) of the original processing capacity).

A third embodiment of the correlation system 1 according to theinvention is advantageous in that said correlation system 1 comprises adown-sampler 5 for generating said input signal and coupled to an outputof an analog-to-digital converter 12 for, in dependence of saidcomparison result, down-sampling an output signal of saidanalog-to-digital converter 12 with a down-sampling factor.

By introducing said down-sampler 5, like for example a memory forstoring y

nples and for reading out y/2 or y/4 or y/8 etc. samples, or like forexample a switch for

ing pass every second or fourth or eighth etc. sample and for blockingall other samples,

information compactness (information density) can be controlled easily.

A fourth embodiment of the correlation system 1 according to theinvention is

antageous in that said down-sampling factor is decreased for a nextcorrelation to increase

d information compactness for said next correlation.

By decreasing said down-sampling factor for next correlations, like for

ample from a factor eight via a factor four and a factor two to a factorone, said

ormation compactness (information density) for these next correlationsis increased. Said

creasing of said down-sampling factor corresponds with increasing adown-sampling

e/frequency, due to said down-sampling factor and said down-samplingrate/frequency

ing reciprocal. The minimum value of the down-sampling factor is one,which means that

e maximum value of the down-sampling rate/frequency is equal to the fullover-sampling

e/frequency. Together with said selection of said smaller parts, theiterative correlations

e now performed in the most optimal way. Of course, after thedown-sampling factor has

ached its minimum value one, the down-sampling rate/frequency will bekept equal to this

ll over-sampling rate/frequency, with further selections of smallerparts still belonging to

e possibilities and therefore not to be excluded.

For each one of said embodiments, said next correlation will generallybut not exclusively be a subsequent correlation. So, it is not to beexcluded that one or more further correlations are situated between aprevious correlation and a next correlation.

The invention is based upon an insight, inter alia, that complicatedcorrelations can be replaced by less complicated iterative correlations,and is based upon a basic idea, inter alia, that the complexity of acorrelation can be amended by adapting the information compactness(information density).

The invention solves the problem, inter alia, of providing a correlationsystem as defined before which requires less processing capacity.

So, more practically, a radio signal arriving via said antenna issupplied to receiver 11 and converted into an analog input signal, whichby analog-to-digital converter 12 is digitised into a digital inputsignal. These signals comprise a code signal like a synchronisationcode, which is repeatedly transmitted and which must be detected forsynchronisation purposes. To be able to make this detection, without anyprior knowledge apart from the code signal itself, the digital inputsignal is correlated with said code signal through correlation system 1,with said code signal being stored in a terminal's memory for exampleforming part of controller 3. Analog-to-digital converter 12 for exampleover-samples the analog input signal with a frequency of for examplefour times the frequency corresponding with a chip period, for exampleto allow large noise-fluctuations and/or large phase-fluctuations in theradio signal to be dealt with. As a result, the digital input signalcomprises four times more samples, which requires a large processingcapacity when correlating such a received signal with a stored signal.This four times over-sampling rate/frequency is minimally necessary fordown-link synchronisation in the UMTS-FDD system. By the end of thecorrelation procedure, the final sampling rate/frequency must be fourtimes the frequency corresponding with a chip period (so when thedown-sampling factor is equal to one), to meet system requirements. Inthe TD-SCDMA system, the final sampling rate/frequency must be minimallyeight times the frequency corresponding with a chip period (so when thedown-sampling factor is equal to one), to meet system requirements.

To reduce the processing capacity, between receiver 11 andanalog-to-digital converter 12 on the one hand and correlator 2 on theother hand, down-sampler 5 has been introduced. Down-sampler 5 forexample comprises a memory for, per predefined time-interval for exampledefining a predefined part of said digital input signal, storing ysamples and for reading out y/4 or y/2 or y samples respectively, orcomprises for example a switch for letting pass every fourth or secondor each sample respectively and for blocking all other samples, tocontrol the information compactness (information density) easily. For afirst correlation, every fourth sample of all samples originating fromand/or stored in analog-to-digital converter 12 is selected for makingone or more sliding correlations via correlator 2. Thereby it should benoted that either every fourth sample of said code signal should be usedor the other three out of four samples of the input signal should bedefined to be equal to zero. Comparator 4, in addition to a comparisonsection further for example comprising a power measurement sectionand/or a power calculation section and/or an averaging section and/or apeak detection section, compares a first correlation result with one ormore thresholds for example generated by controller 3, with a firstcomparison result being supplied to controller 3.

In response to this first comparison result, controller 3, comprising aselection section, selects smaller parts within said predefined part,with said smaller parts for example to be called windows. For examplefour windows each comprising a peak exceeding said one or morethresholds are selected, with each window for example being 10% or 1% ofthe predefined part. Controller 3 informs correlator 2 of these windowsto be used for a second correlation, and further comprises an adaptingsection for adapting the information compactness (information density)such that for said second correlation, every second sample of allsamples originating from and/or stored in analog-to-digital converter 12is selected for making one or more sliding correlations via correlator2, but now just for said four windows. Controller 3 informs down-sampler5, said second correlation comprising one or more sliding correlationsis made, and comparator 4 compares a second correlation result with oneor more thresholds for example generated by controller 3, with a secondcomparison result being supplied to controller 3.

In response to this second comparison result, controller 3 selectseither yet smaller parts within said smaller parts (windows) or selectsa few (for example two out of four) of said smaller parts (windows) tobe used for a third correlation. For example four windows eachcomprising a peak exceeding said one or more thresholds are selected,with each window for example being 1% or 0.1% of the predefined part, ortwo out of four windows are selected. Controller 3 informs correlator 2of these recently defined new windows to be used for a thirdcorrelation, and further adapts the information compactness (informationdensity) such that for said third correlation, every sample of allsamples originating from and/or stored in analog-to-digital converter 12is selected for making one or more sliding correlations via correlator2, but now just for said recently defined windows. Controller 3 informsdown-sampler 5, said third correlation comprising one or more slidingcorrelations is made, and comparator 4 compares a third correlationresult with one or more thresholds for example generated by controller3, with a third comparison result being supplied to controller 3. Forexample at the hand of this third comparison result, the final result ischosen, as a result of which mobile terminal 10 is synchronised with thebase station.

Then, for example in case of the mobile terminal 10 needing to identifythe cell in which it is located, spreading codes are sent from basestation to mobile terminal 10, which are detected through correlator 2again by making sliding correlations, thereby using or not usingdown-sampler 5. As soon as said spreading codes have been identified,controller 3 supplies these codes to decoder 13 for example comprising adespreader section, after which detector 14 for example comprising apilot symbol assisted coherent detection section and/or a rake receiversection can generate (reconstruct) data transmitted from base station tomobile terminal 10.

Alternatively and/or in addition to using down-sampler 5, theinformation compactness (information density) of the input signal couldbe adapted by adapting the over-sample frequency used byanalog-to-digital converter 12, and/or by placing (integrating) anotherdown-sampler into analog-to-digital converter 12, which then need to becontrolled by controller 3.

Usually the code signal in the radio signal and the input signal isrepeatedly transmitted from base station to mobile terminal 10, but itis not to be excluded that, in other systems, such a code signal is sentonly once, and then being stored in mobile terminal 10, for example in abuffer in receiver 11 and/or in analog-to-digital converter 12.

Each block shown or not shown, can be 100% hardware, 100% software or amixture of both. Each block shown or not shown can be integrated witheach other block shown and/or not shown. Especially correlation system 1can be integrated advantageously due to comprising a lot of digitalsignal processing technology. Said receiver 11, analog-to-digitalconverter 12, decoder 13 and detector 14 may each comprise their ownprocessor and/or memory, buffer etc. or may use (arts of) correlationsystem 1. And parts of correlation system 1 may comprise their ownprocessor and/or memory, buffer etc.

In the flow chart shown in FIG. 2 for elucidating a method according tothe invention and a processor program product according to theinvention, the following blocks have the following meaning:

-   -   Block 100: Start; goto 101;    -   Block 101: Reduce the information compactness (information        density) of at least a part of said input signal and/or of at        least a part of said code signal, for example by introducing a        down-sampling factor; goto 102;    -   Block 102: Correlate at least a part of said input signal with        at least apart of said code signal for the given information        compactness (information density) and for one or more given        windows and compare one or more correlation results with one or        more thresholds; goto 104;    -   Block 104: Is the information compactness (information density)        standard, due to for example said down-sampling factor being        equal to one? If yes, goto 105, if no, goto 103;    -   Block 103: Increase the information compactness (information        density) of at least a part of said input signal and/or of at        least a part of said code signal, for example by decreasing said        down-sampling factor (or increasing the reciprocal down-sampling        rate/frequency), and select windows within said part of said        input signal in dependence of one or more comparison results;        goto 102;    -   Block 105: Choose the best comparison result as the final        result, the mobile terminal is now synchronised; goto 106;    -   Block 106: Stop.

The method according to the invention for correlating at least a part ofan input signal with at least a part of at least one code signal ischaracterised in that said method comprises the step of controlling saidcorrelating for performing iterative correlations and for adapting atleast an information compactness of at least a part of at least one ofsaid signals for a next correlation. And the processor program productaccording to the invention for correlating at least a part of an inputsignal with at least a part of at least one code signal, characterisedin that said processor program product comprises the function ofcontrolling said correlating for performing iterative correlations andfor adapting at least an information compactness of at least a part ofat least one of said signals for a next correlation. Said steps andfunctions are for example as follows:

A first step/function comprises the starting of said method/processorprogram product (Block 100). Then, a second step/function involves thereducing of the information compactness (information density) of atleast a part of said input signal and/or of at least a part of said codesignal, for example by introducing a down-sampling factor (Block 101). Athird step/function comprises the correlating of at least a part of saidinput signal with at least a part of said code signal for the giveninformation compactness (information density) and for one or more givenwindows and the comparing of one or more correlation results with one ormore thresholds (Block 102). A fourth step/function involves thechecking whether the

rmation compactness (information density) is standard or not, due to forexample said

vn-sampling factor being equal to one or not (Block 104). If no, afourth step/function

oprises the increasing of the information compactness (informationdensity) of at least a

t of said input signal and/or of at least a part of said code signal,for example by

reasing said down-sampling factor (or increasing the reciprocaldown-sampling

/frequency), and the selecting of windows within said part of said inputsignal in

endence of one or more comparison results (Block 103), which is followedby said third

/function, but now with updated information, etc. If yes, a nextstep/function involves the

osing of the best comparison result as the final result, the mobileterminal is now

chronised (13lock 105). Then, a following final step/function comprisesthe ending of said

thod/processor program product (Block 107).

Of course, further steps/functions are not to be excluded, like forexample a

mting step/function for counting the number of loops made to avoid theinfinite looping,

l like for example a comparing step/function for comparing comparisonresults with each for finding out howmuch progress is made, and like forexample an updating action for updating thresholds, etc.

1. Correlation system (1) for correlating at least a part of an inputsignal with at least a part of at least one code signal, characterisedin that said correlation system (1) comprises a controller (3) forcontrolling said correlation system (1) for performing iterativecorrelations and for adapting at least an information compactness of atleast a part of at least one of said signals for a next correlation. 2.Correlation system (1) according to claim 1, characterised in that saidcorrelation system (1) comprises a comparator (4) for comparing acorrelation result with at least one threshold and in responsegenerating a comparison result, with said controller (3), in dependenceof said comparison result, selecting smaller parts within said part ofsaid input signal for a next correlation.
 3. Correlation system (1)according to claim 2, characterised in that the information compactnessof at least said smaller parts is increased for a next correlation. 4.Correlation system (1) according to claim 3, characterised in that saidcorrelation system (1) comprises a down-sampler (5) for generating saidinput signal and coupled to an output of an analog-to-digital converter(12) for, in dependence of said comparison result, down-sampling anoutput signal of said analog-to-digital converter (12) with adown-sampling factor.
 5. Correlation system (1) according to claim 4,characterised in that said down-sampling factor is decreased for a nextcorrelation to increase said information compactness for said nextcorrelation.
 6. Mobile terminal (10) with down-link synchronisationthrough detection of at least one code signal, which mobile terminal(10) comprises a receiver (11) for receiving a radio signal and forconverting said radio signal into an input signal and comprises acorrelation system (1) coupled to said receiver (11) for correlating atleast a part of said input signal with at least a part of at least onecode signal, characterised in that said correlation system (1) comprisesa controller (3) for controlling said correlation system (1) forperforming iterative correlations and for adapting at least aninformation compactness of at least a part of at least one of saidsignals for a next correlation.
 7. Mobile terminal (10) according toclaim 6, characterised in that said correlation system (1) comprises acomparator (4) for comparing a correlation result with at least onethreshold and in response generating a comparison result, with saidcontroller (3), in dependence of said comparison result, selectingsmaller parts within said part of said input signal for a nextcorrelation.
 8. Mobile terminal (10) according to claim 7, characterisedin that the information compactness of at least said smaller parts isincreased for a next correlation.
 9. Mobile terminal (10) according toclaim 8, characterised in that said correlation system (1) comprises adown-sampler (5) for generating said input signal and coupled to anoutput of an analog-to-digital converter (12) for, in dependence of saidcomparison result, down-sampling an output signal of saidanalog-to-digital converter (12) with a down-sampling factor.
 10. Mobileterminal (10) according to claim 9, characterised in that saiddown-sampling factor is decreased for a next correlation to increasesaid information compactness for said next correlation.
 11. Method forcorrelating at least a part of an input signal with at least a part ofat least one code signal, characterised in that said method comprisesthe step of controlling said correlating for performing iterativecorrelations and for adapting at least an information compactness of atleast a part of at least one of said signals for a next correlation. 12.Processor program product for correlating at least a part of an inputsignal with at least a part of at least one code signal, characterisedin that said processor program product comprises the function ofcontrolling said correlating for performing iterative correlations andfor adapting at least an information compactness of at least a part ofat least one of said signals for a next correlation.
 13. Method fordown-link synchronisation through detection of at least one code signal,which method comprises the steps of receiving a radio signal and ofconverting said radio signal into an input signal and of correlating atleast a part of said input signal with at least a part of at least onecode signal, characterised in that said method comprises the step ofcontrolling said correlating for performing iterative correlations andfor adapting at least an information compactness of at least a part ofat least one of said signals for a next correlation.